2,416 research outputs found
Theory of Optical Tweezers
We derive a partial-wave (Mie) expansion of the axial force exerted on a
transparent sphere by a laser beam focused through a high numerical aperture
objective. The results hold throughout the range of interest for practical
applications. The ray optics limit is shown to follow from the Mie expansion by
size averaging. Numerical plots show large deviations from ray optics near the
focal region and oscillatory behavior (explained in terms of a simple
interferometer picture) of the force as a function of the size parameter.
Available experimental data favor the present model over previous ones.Comment: 4 pages, 3 figure
Optical application and measurement of torque on microparticles of isotropic nonabsorbing material
We show how it is possible to controllably rotate or align microscopic
particles of isotropic nonabsorbing material in a TEM00 Gaussian beam trap,
with simultaneous measurement of the applied torque using purely optical means.
This is a simple and general method of rotation, requiring only that the
particle is elongated along one direction. Thus, this method can be used to
rotate or align a wide range of naturally occurring particles. The ability to
measure the applied torque enables the use of this method as a quantitative
tool--the rotational equivalent of optical tweezers based force measurement. As
well as being of particular value for the rotation of biological specimens,
this method is also suitable for the development of optically-driven
micromachines.Comment: 8 pages, 6 figure
Phi Mesons from a Hadronic Fireball
Production of mesons is considered in the course of heavy-ion
collisions at SPS energies. We investigate the possible difference in momentum
distributions of mesons measured via their leptonic () and
hadronic () decays. Rescattering of secondary kaons in the dense hadron
gas together with the influence of in-medium kaon potential can lead to a
relative decrease of a yield observed in the hadronic channel. We
analyze how the in-medium modifications of meson properties affect apparent -
reconstructed momentum distributions of mesons. Quantitative results are
presented for central Pb+Pb collisions at .Comment: style Revtex4,9 pages, 5 figures. submitted to Phys. Rev.
Coherent atomic beam splitter using transients of a chaotic system
A coherent atomic beam splitter can be realized using the transient dynamics of a chaotic system. We have experimentally observed such an effect using ultracold rubidium atoms. Our experimental results are in good agreement with numerical simulations of the Schrödinger equation for the syste
Resonances and fluctuations at SPS and RHIC
We perform an analysis of preliminary data on hadron yields and fluctuations
within the Statistical hadronization ansatz. We describe the theoretical
disagreements between different statistical models currently on the market, and
show how the simultaneous analysis of yields and fluctuations can be used to
determine if one of them can be connected to underlying physics. We perform
such an analysis on preliminary RHIC and SPS A-A data that includes particle
yields, ratios and event by event fluctuations. We show that the equilibrium
statistical model can not describe the fluctuation measured at RHIC and
SPS, unless an unrealistically small volume is assumed. Such small volume then
makes it impossible to describe the total particle multiplicity. The
non-equilibrium model,on the other hand, describes both the fluctuation
and yields acceptably due to the extra boost to the fluctuation provided
by the high pion chemical potential. We show, however, that both models
significantly over-estimate the fluctuation measured at the SPS, and
speculate for the reason behind this.Comment: Presented at Hot Quarks, 2006 In press, European Physical Journal
Strange Hadron Resonances and QGP Freeze-out
We describe how the abundance and distribution of hyperon resonances can be
used to probe freeze-out conditions. We demonstrate that resonance yields allow
us to measure the time scales of chemical and thermal freeze-outs. This should
permit a direct differentiation between the explosive sudden, and staged
adiabatic freeze-out scenarios.Comment: 8 pages including 4 figures, in Proceedings of Strange Quark Matter
2001, Frankfurt, submitted to J. Phys. G version 2: refernces
corrected/added, numercial corrections in figures 2,3,
Developing an intervention to facilitate family communication about inherited genetic conditions, and training genetic counsellors in its delivery.
Many families experience difficulty in talking about an inherited genetic condition that affects one or more of them. There have now been a number of studies identifying the issues in detail, however few have developed interventions to assist families. The SPRinG collaborative have used the UK Medical Research Council's guidance on Developing and Evaluating Complex Interventions, to work with families and genetic counsellors (GCs) to co-design a psycho-educational intervention to facilitate family communication and promote better coping and adaptation to living with an inherited genetic condition for parents and their children (<18 years). The intervention is modelled on multi-family discussion groups (MFDGs) used in psychiatric settings. The MFDG was developed and tested over three phases. First focus groups with parents, young people, children and health professionals discussed whether MFDG was acceptable and proposed a suitable design. Using evidence and focus group data, the intervention and a training manual were developed and three GCs were trained in its delivery. Finally, a prototype MFDG was led by a family therapist and co-facilitated by the three GCs. Data analysis showed that families attending the focus groups and intervention thought MFDG highly beneficial, and the pilot sessions had a significant impact on their family' functioning. We also demonstrated that it is possible to train GCs to deliver the MFDG intervention. Further studies are now required to test the feasibility of undertaking a definitive randomised controlled trial to evaluate its effectiveness in improving family outcomes before implementing into genetic counselling practice.The National Institute of Health Research funded the study but any views expressed do not necessarily reflect those of the Authority. Funded by NIHR reference number: RP-DG-1211-10015
Projectile fragmentation of 129Xe at Elab=790 AMeV
We have measured production yields and longitudinal momentum distributions of
projectile-like fragments in the reaction 129Xe + 27Al at an energy of Elab=790
AMeV. Production cross sections higher than expected from systematics were
observed for nuclei in the neutron-deficient tails of the isotopic
distributions. A comparison with previously measured data from the
fragmentation of 136Xe ions shows that the production yields strongly depend on
the neutron excess of the projectile with respect to the line of
beta-stability. The momentum distributions exhibit a dependence on the fragment
neutron-to-proton ratio in isobaric chains, which was not expected from
systematics so far. This can be interpreted by a higher excitation of the
projectile during the formation of neutron-deficient fragments.Comment: 21 pages, 8 figures, 1 tabl
A comparison of statistical hadronization models
We investigate the sensitivity of fits of hadron spectra produced in heavy
ion collisions to the choice of statistical hadronization model. We start by
giving an overview of statistical model ambiguities, and what they tell us
about freeze-out dynamics. We then use Montecarlo generated data to determine
sensitivity to model choice. We fit the statistical hadronization models under
consideration to RHIC data, and find that a comparison fits can shed
light on some presently contentious questions.Comment: Proceedings for SQM2003 [7th Int. Conf. on Strangeness in Quark
Matter (Atlantic Beach, NC, USA, Mar 12-17, 2003)], to be published in
Journal of Physics G (Typos corrected, reference added
Dynamics and freeze-out of hadron resonances at RHIC
Yields, rapidity and transverse momentum spectra of ,
, and the meson resonances ,
, and are predicted. Hadronic rescattering leads to a
suppression of reconstructable resonances, especially at low . A mass
shift of the of 10 MeV is obtained from the microscopic simulation, due
to late stage formation in the cooling pion gas.Comment: Proceedings of the Strange Quark Matter 2003, eprint version differs
from published versio
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